Return flow boiler

ABSTRACT

In return flow boilers the gases flowing along the wall of the flue tube will be cooled, whereby the combustion in the marginal portions of the flame will be considerably less complete than in the core thereof, which will have undesirable consequences when the flame emerges into the return chamber. In order to bring about a complete combustion also of the marginal portions of the flame the outlet of the flue tube is considerably restricted as compared to the main part of the tube, whereby the portions of the flame having flown along the wall of the flue tube will be forced into the core of the flame, when this emerges into the return chamber.

Feb. 1, 1972 United States Patent ()stbo 2,383,924 8/1945 Wayeta1...............................122/182 [54] RETURN FLOW BOILER 1,755,949 4/1930 Clarks0n.... 2,568,781 9/1951 Watts....................................122/182 Inventor: Nils Axel Ambjorn Ostbo, Goteborg,

Sweden Primary Examiner-Kenneth W. Sprague Pierce, Schefiler & Parker ow mm b m mo G \h mm ML W 2.. M m w mm hm HE mt a oe GH [73] Assignee:

Attorney Sweden [57] ABSTRACT In return flow boilers the gases flowing along the wall of the flue tube will be cooled, whereby the combustion in the mar- [22] Filed: Apr. 6, 1970 ginal portions of the flame will be considerably less complete than in the core thereof, which will have undesirable consequences when the flame emerges into the return chamber. In order to bring about a complete combustion also of the marginal portions of the flame the outlet of the flue tube is considerably restricted as compared to the main part of the tube, whereby the portions of the flame having flown along the wall of the flue tube will be forced into the core of the flame, when this emerges into the return chamber.

1 Claims, 1 Drawing Figure References Cited UNITED STATES PATENTS 1,936,623 Frentzel, .lr. 122/ l 82 t) m t) m .I I I I h n f\ 1 m N 5 I RETURN FLOW BOILER BACKGROUND OF THE INVENTION lt is difiicult to bring about a complete combustion of fuel oil in a boiler furnace. This incomplete combustion causes contamination of the heat exchanger surfaces in the boiler and also sanitary inconveniences due to partly burnt particles following the gases into the atmosphere.

SUMMARY OF THE INVENTION The present invention refers to a return flow boiler having a flue tube connected centrally to one sidewall of a return chamber and is surrounded by a number of fire tubes running backwards therefrom, parallel to the flue tube, which is designed with a specific object to aid the complete combustion of the fuel oil. The invention is characterized by that the outlet of the flue tube into the return chamber is noticeably smaller than the cross section of the main part of the flue tube, in such a manner that the marginal portions of the flame within the flue tube will be forced into the core of the flame, when the latter passes out into the return chamber.

BRIEF DESCRIPTION OF THE DRAWING One embodiment of the invention is shown on the accompanying drawing, which is a section through a vertical hot water boiler.

DESCRIPTION OF THE PREFERRED EMBODIMENT The boiler comprises a vertical, cylindrical shell to the upper part of which an oil burner is fitted. The burner is directed into a flue tube 11, which is arranged centrally within the shell, and is connected to one sidewall ofa return chamber 12. A number of fire tubes 13 extend from this chamber backwards, parallel to the flue tube and open into a collecting chamber 14, which is connected to an outlet 15 for the combustion gases. The water enters at 16 and leaves the boiler at 17v The return chamber 12 has a cup-shaped lower end wall 18 designed as a water chamber, to the perimeter of which a circular row of closely arranged water tubes, preferably provided with fins is arranged the tubes, or fins respectively, being interconnected to form a gastight sidewall in the return chamber, said sidewall being subjected to radiation from a flame entering the chamber.

The fire tubes 13 are fitted into two end plates 20, which together with the cylindrical shell 21 enclose a convection part. The water flowing within the latter is guided by baffles 22 arranged in a suitable manner. The water tubes 19 are connected to the lower end plate 20 outside the fire tubes 13. The latter are mounted symmetrically around the flue tube and the temperature will be mainly uniform within this part of the boiler.

The flame passes from the flue tube out into the return chamber through an outlet 23, the cross section of which is noticeably smaller than the cross section of the main portion of the flue tube. In this manner the marginal portions of the flame, which have been in contact with the cooled wall of the flue tube and therefore have a lower temperature than the rest of the flame, are forced into the core of the flame, whereby an efficient combustion of the particles entrained in the marginal portions of the flame is efficiently obtained. The resulting gases are symmetrically distributed in the return chamber and flow through the fire tubes towards the outlet 15. The outlet 23 of the flue tube is cylindrical over a short distance. The portion between the cylindrical main part of the flue tube and the outlet portion is basically a truncated cone having its apex 26 located just outside the outlet, the wall of the transient portion is slightly curved to ensure a smooth flow. A number of guide vanes 27 may be fitted in the cylindrical portions to impart a swirling motion to the flame entering the return chamber, whereby particles of ash and other contaminations are separated by centrifugal action. Such articles are collected at the bottom of the return cham er and may be removed through a cleaning opening 24.

If circulation pumps are used the flow of water within the boiler may be reversed. The boiler may be arranged with its longitudinal axis horizontal and by the fitting of a steam drum the boiler may be used as a common steam boiler.

What I claim is:

l. A return flow boiler having a flue tube connected centrally to one sidewall of a return chamber and being surrounded by a number of fire tubes running backwards therefrom and parallel to the flue tube, a fuel burner being fitted at the end of the flue tube remote from the return chamber and being arranged to direct flame axially into said fire tube, in which the main part of the flue tube is cylindrical and presents a smooth, water-cooled, wall towards the flame, and the outlet of the flue tube is cylindrical over a short distance and noticeably smaller than the cross section of the main part of the flue tube, the transient part between said cylindrical portions being shaped as a truncated cone having its apex just outside the outlet from the flue tube and likewise presenting a smooth, water-cooled wall towards the flame, whereby the marginal portions of the flame within the flue tube will be forced into the core of the flame, when the latter passes out into the return chamber. 

1. A return flow boiler having a flue tube connected centrally to one sidewall of a return chamber and being surrounded by a number of fire tubes running backwards therefrom and parallel to the flue tube, a fuel burner being fitted at the end of the flue tube remote from the return chamber and being arranged to direct flame axially into said fire tube, in which the main part of the flue tube is cylindrical and presents a smooth, water-cooled, wall towards the flame, and the outlet of the flue tube is cylindrical over a short distance and noticeably smaller than the cross section of the main part of the flue tube, the transient part between said cylindrical portions being shaped as a truncated cone having its apex just outside the outlet from the flue tube and likewise presenting a smooth, water-cooled wall towards the flame, whereby the marginal portions of the flame within the flue tube will be forced into the core of the flame, when the latter passes out into the return chamber. 